Why does my core speed up at idle?

I'm starting to do some overclocking with my core i5 750 and ASUS P7P557D Pro according to THIS TUTORIAL


So far I set the DDR3 frequency to 1600 and increased the BCLK frequency to 144MHz.


The weird thing is that when I run CPU-Z and watch it while running Prime95 to stress the system the core speed is faster when at idle. As soon as Prime95 starts, it slows down.

Here is the CPU-Z at stress:


Here is CPU-Z at idle:


I don't understand?

Shouldn't the core slow down at idle?

When stressing all cores on the CPU the turbo only goes so high on all four cores. However when you only have one core being utilized with any load it will go much faster. That is how Turbo Boost works.

And there is no such thing as idle. You may be idle but the computer rarely is.